minimum height for laundry standpipe?

Under UPC the laundry standpipe p-trap must be: 6" <= floor <= 18"
Q1: where is the measurement taken from w/ regard to the p-trap? In Peter Hemp's book it shows it as the connection point between the standpipe (above) and the p-trap (as opposed to the weir or dead bottom of the p-trap, to name to other obvious points of reference). Is Hemp's drawing correct?

Under UPC the laundry standpipe top must be: 18" <= p-trap <= 30"
Q2: is the aim of these two restrictions to end up with the standpipe at 36"? One interpretation would be that if the p-trap is 6" from floor, standpipe should be 30" from p-trap, and if p-trap is 18" from floor standpipe should be 18" from p-trap... this is NOT what the code says, but is that what it means to say?

OR to put it another way...
Q3+: what is the recommended height above the floor for the top of the standpipe? Should it be above the flood level of the washer (as I've seen mentioned in one resource)? Can it be "hidden" behind the machine (for aesthetics) or does it need/want to be above the machine?

If you search, this has probably already been answered several times by now.

804.1 All plumbing fixtures or other receptors
receiving the discharge of indirect waste pipes shall be
approved for the use proposed and shall be of such
shape and capacity as to prevent splashing or flooding
and shall be located where they are readily accessible
for inspection and cleaning. No standpipe receptor for
any clothes washer shall extend more than thirty (30)
inches (762 mm), nor less than eighteen (18) inches
(457 mm) above its trap. No trap for any clothes
washer standpipe receptor shall be installed below the
floor, but shall be roughed in not less than six (6)
inches (152 mm) and not more than eighteen (18)
inches (457 mm) above the floor.

The top of the standpipe MUST be above the FLR of the appliance no matter what, and it sounds like your code wants a minimum dimension of 18", and a maximum dimension of 30", for the standpipe dimension. That's more than enough information to figure out what you have to do.

All of the machines I am familiar with have a control panel on the back that extends above the level of the tub. This would allow the standpipe to extend above the top of the tub and still be hidden. That would put the height somewhere around 36". I hope you know the drain is supposed to be 2" pipe. In years past, 1-1/2" was enough, but new machines empty the water much faster than a 1-1/2" pipe can accommodate.

OK thanks, the FLR is the key determinant then for the overall height. Yes I am running 2" pipe. BUT no one has indicated what the point of reference is for the p-trap height to be measured as being 6" above the floor... what part of the p-trap must be > 6" from floor?

I put the trap somewhere between 6" and 18", and the standpipe at 42". That puts the box at a point where the valves are accessible, in case the homeowner is one of those "three people in America" who acutally turn the valves off after every wash.

I know this thread is a bit old and you may never read this, but thanks so much for actually quoting and referencing the applicable code. I spent several frustrating hours searching various forums and threads, finding lots of statements, but no code references to back them up. I am trying to figure out how to plumb in a washing machine in a daylight basement which is part of a large addition/remodel to my house. Originally the laundry was to be on the other side of the wall on the main level and the plumbing would have been easy, but we decided to move the laundry to the basement part way through the project. Unfortunately we are a few inches too low to put the trap in the wall easily. At least now that I am able to find the exact requirement in the 2011 Oregon Plumbing specialty code, I know the exact limitations I have to work around.

If you search, this has probably already been answered several times by now.

804.1 All plumbing fixtures or other receptors
receiving the discharge of indirect waste pipes shall be
approved for the use proposed and shall be of such
shape and capacity as to prevent splashing or flooding
and shall be located where they are readily accessible
for inspection and cleaning. No standpipe receptor for
any clothes washer shall extend more than thirty (30)
inches (762 mm), nor less than eighteen (18) inches
(457 mm) above its trap. No trap for any clothes
washer standpipe receptor shall be installed below the
floor, but shall be roughed in not less than six (6)
inches (152 mm) and not more than eighteen (18)
inches (457 mm) above the floor.

The top of the standpipe MUST be above the FLR of the appliance no matter what, and it sounds like your code wants a minimum dimension of 18", and a maximum dimension of 30", for the standpipe dimension. That's more than enough information to figure out what you have to do.